1. Field of the Invention
The invention pertains to a guide for the piston rod of a piston-cylinder assembly, especially for a vibration damper, a shock-absorbing strut, or a level-control device, where the guide has a guide body with an outer end surface, where the body holds a piston rod seal, and where the piston rod is installed in the guide and sealed with freedom of axial movement.
2. Description of the Related Art
DE 198 13 240 discloses a guide for a piston rod in which the guide serves to guide a piston rod moving in a cylinder, the guide holding a seal for the piston rod. A guide sleeve, a stripper, and a stripping lip are also parts of the structural unit. The piston rod seal is provided on its outer surface with an O-ring, which serves as a clamping ring; two of these sealing units can be arranged in a row in the axial direction. The disadvantage here is that the entire axial length of the O-ring presses against the piston rod seal, so that, at the planned operating pressures of, for example, 50-150 bars in a level-control element, a seal of this type suffers increased wear and thus does not offer the desired long-term durability. In addition, high coefficients of friction, which are not acceptable in practice, are observed at these high operating pressures.
Against this background, it is the object of the invention to create a guide for a piston rod with a piston rod seal, in which the seal operates not only with low friction but also without any leakage of oil.
This object is achieved in that the piston rod seal has an axial extension which passes around at least part of the circumference and which is located on the end opposite the interior space of the piston-cylinder assembly. This extension is held in a recess which is spaced from the piston rod and coaxial to it. The piston rod seal is thus supported on the end facing away from the pressure in the recess provided in the guide body so that this part of the piston rod seal is not pressed against the surface of the piston rod as a result of the static and dynamic pretension of the O-ring. It is advantageous for the essential and necessary pressure to be limited to the area of the sealing edge.
In accordance with another feature, the piston rod seal is provided with an O-ring on the radially outer circumferential surface, i.e., on the side opposite the sealing edge.
In an embodiment which is favorable in terms of production technology, the extended area passes all the away around the circumference. It is thus sufficient merely to introduce an annular channel into the guide body by means of a turning operation. The seal then engages in this channel and is supported radially with respect to the piston rod by the inside wall of the channel.
In accordance with an essential feature of the invention, an angled relief is provided between the piston rod and the piston rod seal, which relief starts from the sealing edge and extends in the direction of the axial extension as an inward facing frusto-conical surface. In this design it is advantageous that, as a result of the way in which the piston rod seal is supported, the relief remains almost completely preserved even at high internal operating pressures of the piston-cylinder assembly, and thus the return of leakage oil is ensured, regardless of the pressure.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.